Method and apparatus for enhancing filter bed performance

ABSTRACT

In a vessel containing a filter bed and containing a mixed liquor containing suspended solids, a system disturbs/dislodges a sludge mat that settles on the filter bed. Thus, the system controls the sludge mat on the filter bed that otherwise may blind the filter bed and significantly reduce or stop process liquid flow into and through the filter bed. The system helps maintain effective vessel effluent flowrates with reduced requirements for filter bed backwashing or other filter bed maintenance. The system includes a sludge mat dislodging member that moves along the filter bed surface, preferably on but substantially not inside the filter bed, to disrupt/dislodge the sludge mat and/or prevent formation of the sludge mat. Preferably, the dislodging member is carried inside the vessel on a moving arm or arms that rotate in a plane parallel to the filter bed surface. The preferred sludge mat dislodging member(s) hang from the rotating arm(s) to slide along the top of the filter bed through the sludge mat. The sludge mat control methods and apparatus preferably are used during normal operation of the reactor/vessel, without requiring shutdown or interruption of the process. The methods and apparatus may be effective in sludge blanket microbial remediation reactors that require high flowrates of liquid effluent due to low residence times in a given vessel.

This application claims priority of provisional application Ser. No.60/401,267, entitled “Method and apparatus for Improving the Withdrawlof Liquid from a Settled Bed of Solid Particles in a Microbial Reactor,”filed Aug. 4, 2002, which is incorporated herein by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates, generally, to apparatus and methods of operationfor a filter bed installed in a microbial remediation reactor or inother chemical, petrochemical, waste, or food process vessels. Morespecifically, the invention relates to improvement of filter bedperformance by moving and/or preventing formation of the sludge mat thattends to settle on top of the filter bed surface, so that the sludge matdoes not block flow through the filter bed to an extent that requirespremature backwashing of the filter bed.

2. Background Art

The instant invention is particularly effective in, but is not limitedto, downflow sludge blanket reactors used for microbial remediation ofvarious wastewater streams. For example, the instant invention may beeffective for treating streams comprising activated sludge; fats, oils,and grease (“FOG”); suspended BOD solids; and soluble BOD; such as flowfrom municipal waste plants or food and meat processing plants. Theinvention is particularly effective in optimizing anaerobic microbialtreatment of high FOG and high total suspended solids (“TSS”) streams,or treatment of lower FOG/TSS streams or soluble BOD streams wherein lowresidence times and the associated high effluent flowrates requireefficient filter bed performance and control of filter bed plugging.Examples of some of the many embodiments of microbial reactors that maybenefit from the instant invention are described in patents to Stormo(U.S. Pat. No. 5,616,304, “Slurry Reactor”; U.S. Pat. No. 5,744,105,“Slurry Reactor”; and U.S. Pat. No. 5,779,996, “Microbial RemediationReactor and Process”; and U.S. Pat. No. 6,346,412, “MicrobialRemediation Reactor and Process”).

The preferred microbial reactor may utilize a diverse population ofsuspended microorganisms (herein “biomass”) to treat the waste andcontaminants contained in the mixed liquor in the reactor (the bulkliquid in the reactor containing suspended and dissolved solids). In thebottom of the preferred downflow reactors is a settled bed of coarsesolids, such as course sand. The sand bed filters reactor liquid as itpasses through the filter bed, and out of the reactor as reactoreffluent. The sand bed filters out the solids (including biomass andother solids) from the reactor liquid, in order to retain the biomass inthe reactor and to retain the waste solids in the reactor for thedesired remediation residence time. Without preventive or remediativemeasures, the sand bed typically becomes plugged with solids, and, indoing so, slows and eventually stops the flow of reactor effluent. Whenflow through the filter bed slows, the conventional solution is to“backwash” the filter bed, by the conventional technique of liquid flowup through the filter bed, or by the technique of stirring andfluidizing the filter bed as discussed below.

U.S. Pat. No. 6,346,412 (“the '412 patent”) teaches the use of a mixingblade P-78 inside the sand bed P-84 as a means to prevent or alleviateplugging of the sand bed. See FIG. 1. Patent '412 teaches that the sandbed “may be used as a filter as the water is removed from the bottom ofthe reactor. Any suspended material, including biomass, is retained bythe sand filter therefore allowing very high biomass densities to bemaintained, with resulting very high activity. As the mixing blade movesthrough the sand bed, it fluidizes the sand near the blade and keeps thebiomass from plugging the sand or the screened outlet.” See screen P-86and outlet P-82 in FIG. 1. Thus, the mixing blade in the sand bed asdescribed in U.S. Pat. No. 6,346,412 performs a “backwash” step, ofunplugging or preventing plugging of the sand bed, by rotating throughthe sand bed to fluidize the sand bed. While this stirring techniquedoes not involve back-washing with up-flow liquid and does not involveemptying the reactor, it does require shutting off the flow out of thereactor, and, hence, is disruptive to the reactor operation andproductivity.

The '412 patent further discloses the use of a sand bed mixing blade inan aerobic reactor, wherein the mixing blade is in the upper region ofthe sand bed, while leaving the lower region of the sand bed relativelyundisturbed. This technique is a means for back-washing the sand bedwhile leaving the lower region of the sand bed as an anaerobicdenitrification region. Still, this technique involves stirring of thesand bed to solve the low/no reactor effluent problem in the reactor.

To rotate a sand bed stirring mechanism, such as embodiments describedin the '412 patent, the horizontal stirrer blade P-78 is supplied withfluid from a central, vertical supply conduit P-76. Fluid preferablypasses through openings at or near the blade's leading side forfluidization, and through openings at or near the blade's trailing sidefor propulsion. The fluidization back-washes the sand, removing solidsfrom the voids in the bed and forcing the solids back up into thereactor. After this back-washing process is performed, movement of thestirring mechanism is preferably stopped and flow of reactor effluentresumes.

In some microbial remediation reactor operations, the effluent flow-ratecan easily be maintained with intermittent fluidization by means of theabove-described in-sand stirrer blade “back-washing” the sand bed.However, the inventors have discovered that in many operations and undermany conditions, the frequency of sand bed backwashing must increase toan extent that makes it difficult to maintain productive operation ofthe reactor, and difficult or impossible to retain sufficient biomass inthe reactor for the desired microbial activity and to retain the wastesolids in the reactor for the residence time required for remediation.

Therefore, there is still a need for improved apparatus and methods foroperating a reactor having a filter bed in such a way that frequentbackwashing of the filter bed is not required to maintain an acceptablerate and quality of reactor effluent discharge. There is a need forapparatus and methods that improve filter bed operation, especially inmoderate BOD applications such as waste-waters having 1000 mg/L BOD and100 TSS up to 50,000 mg/L BOD and 10,000 TSS. Such applications arecharacterized by short residence times on the order of hours, ratherthan days, and consequently the reactors are designed for high effluentflowrates. The filter beds of such applications need to be effective andlong-lived in order to achieve these flowrates. The present inventionmeets these and other needs, as will be clear from the followingdescription, drawings, and claims.

SUMMARY OF THE INVENTION

The present invention comprises methods and apparatus for improvingoperation of a filter bed in a microbial remediation reactor, afiltration vessel, or other process vessel. The invented method andapparatus provide for reducing, dislodging, or otherwise controlling theprocess solids that settle on the filter bed, especially in down-flowoperations as liquid is flowing through the filter bed to be withdrawnfrom below/in the filter bed. The invented method and apparatus comprisedislodging the process solids that settle on top of the filter bed, toprevent the solids from “blinding” the filter bed to an extent thatslows flow into the filter bed an unacceptable amount or that stops flowinto the bed. In some embodiments, the settled solids may serve as thetop layer of a dual-media filtration system comprising the solids andthe filter bed, so that controlling the settled solids by a renewalstep, rather than completely eliminating the settled solids, mayoptimize filtration and biomass retention.

In the preferred embodiments, a dislodging member is moved along the topof the filter bed to dislodge at least a portion of the settled processsolids and uncover at least a portion of the filter bed top surface.This uncovering step allows the process liquid to access the filter bed,so that the liquid may flow through the filter bed as intended. Byutilizing the invented method and/or apparatus, flow is maintainedthrough the filter bed until the filter bed itself is restricted orplugged by solids in the voids in the filter bed. This way, the filterbed capacity is the limiting factor in requiring back-washing of thefilter bed or a shutdown for clean-out, rather than the typicallyquick-settling solids that form the “blinding” mat on top of the filterbed.

The invented methods and apparatus may be used in many process and unitoperation vessels. There may be a process taking place in the vesselabove the filter bed, such as a chemical reaction or microbial process,or, alternatively, filtration through the subject filter bed may be theonly operation taking place in the vessel. In either case, the liquidabove the filter bed may be called herein “process liquid,” and thismeans the bulk of the liquid above the filter bed in the vessel whetherit is involved in a chemical or microbial process or simply feedstockthat flows into the vessel for the unit operation of filtration.

In a preferred embodiment of the invention, the method of dislodgingsettled solids is applied in a down-flow microbial remediation reactor,wherein the reactor contains mixed liquor that comprises various wastematerials, contaminants, and microbes in water. The solids tend tosettle on the filter bed by gravity and by down-flow reactor flowscheme.In such embodiments, the solids tend to form a sludge mat that is dryrelative to the process liquid (“mixed liquor”) above it, and thissludge mat greatly restricts or completely stops liquid flow into thefilter bed, and, hence, greatly restricts or stops reactor effluent. Theinventors have found that even a mat thickness of less than two inchescan severely slow or stop reactor effluent flow.

The preferred apparatus comprises one or more arms carrying dislodgingmembers across the top surface of the bed, preferably on but not in thefilter bed, to contact and move aside the sludge mat in their paths.This moving of the mat “un-blinds” that portion of the filter bed forfurther filtration, allowing continued process liquid flow down into thefilter bed for further filtration and discharge as reactor effluent.Typically, the remediation reactor may operate for an extended time withintermittent or continuous dislodging of the sludge mat and without anystirring or other back-washing of the filter bed itself. Overallproductivity and ease of operation are enhanced with the inventedmethods and apparatus, especially in microbial remediation operationswherein the feed water quality dictates lower residence times and highreactor effluent flowrates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a prior microbial reactor with a sand bed and asand bed stirring blade, according to one embodiment of U.S. Pat. No.6,346,412.

FIG. 2 is a partial cutaway view of one embodiment of the invention,showing a sand bed stirring blade inside the sand bed and one embodimentof the invented sludge mat renewal system comprising a dislodging uniton top of the sand bed.

FIG. 3 is a partial, detail cross-sectional view of the embodiment ofFIG. 2, viewed along line A—A, illustrating an embodiment of a sludgemat renewal paddle trailing from a support arm.

FIG. 4 is a side view of a microbial reactor comprising one embodimentof a sand bed renewal blade plus one embodiment of a sludge mat renewalsystem comprising mat dislodging units.

FIG. 5 is a detail view of a portion of the embodiment of FIG. 4,showing a portion of both the sand bed blade and the sludge matdislodging units.

FIG. 6 is a front view of one of the sludge mat dislodging units ofFIGS. 4 and 5.

FIG. 7 is a top view of the dislodging unit of FIG. 6.

FIG. 8 is an end view of the dislodging unit of FIGS. 6 and 7.

FIG. 9 is a schematic side view of a dislodging member as in FIGS. 4-8,shown in relationship to the sand bed surface.

FIG. 10 shows schematically an alternative embodiment wherein multiplesludge mat renewal modules are installed in a large-diameter reactor.

FIG. 11 shows an alternative embodiment of a vessel with a filter bedutilizing an embodiment of the invention, wherein the vessel is atertiary sewage water treatment filter.

FIG. 12 illustrates data from operation of a sludge blanket reactorhaving a filter bed, both with and without operation of an embodiment ofthe invented sludge mat dislodging methods and apparatus.

FIG. 13 is a plot of the first four hours of data from the operations ofFIG. 12.

FIG. 14 illustrates operation of the sludge blanket reactor of FIGS. 12and 13, with repeated runs comprising operation with an embodiment ofthe invented sludge mat dislodging system, followed by sand bedback-washing with a sand stirring blade, and restart of the operationwith the dislodging system in operation.

DETAILED DESCRIPTION OF THE INVENTION

The Figures and the following description illustrate embodiments of theinvented methods and apparatus for enhancing filter performance, bycontrol or renewal of the top layer in a multilayer filtration system.The preferred process and filter bed are in a down-flow sludge blanketreactor (“SBR”) that remediates wastewater, the name being due to thereactor being full of a “blanket” of “sludge” comprising microbes, wasteproducts such as food waste or sewage upon which the microbes feed, andwater. While the invention may be applied to both aerobic and anaerobicreactors and to many different qualities of waste water, the inventionproves especially beneficial to anaerobic reactors with medium to hightotal suspended solids (TSS) and high fats, oils, and grease (FOG),and/or high soluble BOD.

A filter bed may be installed in a down-flow microbial remediationreactor, to filter solids from the process liquid flowing out as reactoreffluent. This way, the mixed liquor, including the biomass, remains inthe reactor for continued residence time rather than flowing out of thevessel. Thus, the remediation of the waste and contaminants in the mixedliquor continues, and only relatively clean, low BOD (biological oxygendemand) liquid flows out of the reactor. Proper filtration and controlof reactor effluent are factors in maintaining the proper concentrationof microbes and nutrients in the mixed liquor, which is crucial foreffective remediation.

The inventors believe that the filtration media in many embodiments ofdown-flow sludge blanket reactors may be described as a “dual” media.First, and lower in the reactor, is the filter bed comprising coarseparticulate that may be sand, carbon or coal granules, glass beads, orother non-soluble filter media.

In many remediation reactors, the chosen filter bed is very coarse sandor sized like small pebbles, and so may be referred to hereafter as the“sand bed” or “sand filter.” It may be understood that the filter bedparticulate is of a coarseness/size and shape that provide many voidsbetween the particles for receiving and physically trapping solids fromthe reactor. Second, and forming on the top surface of the filter bed,is a layer of settled solids from the process liquid. Both the sludgemat and the filter bed may be beneficial for the operation, because,combined, they can provide excellent filtration for the reactoreffluent. However, the dual media may be operable only to a point atwhich the thickness, density, impenetrability, or other characteristicsof one or the other filter media severely limits liquid flow through thesettled solids/filter bed combination. At this point, the requiredeffluent flowrate may not be maintained, and proper reactor operationmay be jeopardized.

Although the settled solids is believed to be an effective andbeneficial filtration layer in many instances, the settled solids mayalso be the limiting factor in operability of the filtration system. Thesettled solids that may serve as a top layer of filtration media alsomay be a sludge mat of such thickness, density, and relative drynessthat it can greatly reduce or even completely block fluid flow into thefilter bed and, hence, out of the reactor. While the mixed liquor istypically less than 2 wt-% solids in water, the sludge mat is typically2-20 wt-% solids (approximately 20,000-200,000 mg/L solids). Dependingon the reactor operating parameters, feed quality, and target effluentquality of flowrate, the formation of a mat that slows the flow into thefilter bed (and hence the rate of reactor discharge) to an unacceptablylow value may occur before the sand filter is plugged (“loaded” withsolids). In these instances, therefore, the upper layer of filtrationmedia, the sludge mat, becomes the limiting factor before the sand bed.

Therefore, embodiments of the invention comprise methods and apparatusto control the formation of a dual-layered filtration media by reducingor dislodging the sludge mat that forms on the sand bed. Due to thesludge mat being a main factor in slowing effluent rates, the control ofthe sludge mat is particularly important for extending the process runlength before back-washing or shutdown. With proper control or “renewal”of the sludge mat, which may be considered renewal of the filter bedsurface, the run length typically may continue until the filter bedplugs with solids.

The preferred method and apparatus for controlling the sludge matcomprise one or more dislodging members in the top filtration layer,that is, on or very near the top surface of the sand bed, but outsidethe sand bed. The dislodging member comprises a “top-surface” blade,scraper, or other member that disrupts and moves the sludge mat, butdoes not plow or dig significantly into the sand bed. Preferably, thedislodging member does not disrupt or move any of the sand, or, at themost, disrupts the sand very minimally. The dislodging member may movein any direction across the top surface of the filter, powered by one ormore methods, including mechanized (motor) drive, hydraulic propulsion,magnets, or other power means, for example. The preferred direction andmeans are rotation on an axis in a plane parallel and closely above thesand surface. Other directions and means of movement may be used. An armor arms may be connected to the vessel wall rather than being installedcentrally, for example, so that the arm may roll on a wheel or travel ona track on a surface of the vessel. An arm or arms may extend throughthe vessel wall and be powered and controlled on the outside of thevessel, but a seal would be required to close the vessel in spite of thearm(s) movement and this would be difficult.

Propulsion methods for the sludge mat dislodging system may include apropulsion stream directed from the dislodging system in the trailingdirection, with or without a fluidization stream directed from thedislodging system in the leading direction. It is preferred to have allfluid streams associated with moving the dislodging system to bedistanced from the sand surface, and, therefore, distanced from thedislodging member on the sand surface. This may be accomplished byproviding a rotating propulsion arm with fluid nozzles/openings wellabove the sand bed and mechanically and operatively connecting it to therotating arm holding the dislodging member. This placement of thepropulsion arm in the middle of the mixed liquor typically allowspropulsion jets to power the dislodging system without the need forfluidizing jets on the leading-edge of any portion of the arms. Themiddle level of the mixed liquor is typically the least dense region ofthe reactor contents, so that locating the propulsion stream in thismiddle region is particularly effective for providing propulsion,without the need for fluidization and with little or noshredding/pulverizing of the solids in the mixed liquor.

Distancing of the fluid jets from the sludge mat prevents the fluid jetsfrom shredding/disintegrating the sludge mat into very small particles,or even single cells. This, in turn, helps keep the biomass and solidsinside the reactor rather than allowing them to flow out in the reactoreffluent, resulting in high microbial activity and long residence timefor the solids under remediation. When control of the sludge mat is notsufficient to maintain the desired effluent flowrate, back-washing ofthe filter bed may be done by stirring and/or fluidizing the sand bed.One or more sand bed stirring mechanisms may be provided, for example,according to stirring techniques disclosed in U.S. Pat. No. 6,346,412(“the '412 patent”). This way, the reactor employs both a dislodgingmember at or slightly above the sand surface and a stirring mechanisminside the sand bed. The sand bed stirring arm may be powered in variousdirections by various means, such as a motor drive or hydraulicpropulsion. The sand stirrer blade is preferably powered by fluid flow,with a combination of trailing-side propulsion nozzles/openings andleading-side fluidization nozzles/openings. The fluidization nozzlesfluidize the sand in front of the sand stirring blade, which unplugs andcleans the sand and also makes blade rotation easier and less likely toshred the biomass and solids. The fluidization nozzles may be suppliedwith mixed liquor, filtered reactor effluent, or fresh water, forexample.

Preferably, both the dislodging system and the sand bed stirrer bladerotate in the vessel on hydraulically-propelled arms, with movement andcontrol of the two systems being independent of each other. Probably,the dislodging system propulsion and the sand bed stirring propulsionare both supplied by pumping of mixed liquor taken from near the middleof the reactor, but may also be reactor feed, reactor effluent, or freshwater, for example.

The preferred sludge mat dislodging system comprises one or moredislodging members, sweeping along the top surface of the sand bed,temporarily disrupting, dispersing or otherwise moving the mat ofsludge. A plurality of dislodging members may be provided on a singlerotating arm, on front and rear portions of the single rotating arm, oron multiple rotating arms, so that the members reach all areas of thesand surface at some time during the arm(s) rotation. Dislodging memberson multiple arms or arm portions may be radially offset, so that membersrotate all or substantially all across the radius of the sand bed toclear all or substantially all of the sludge mat in a completerevolution of the arms. Less preferably, the dislodging members mayrotate across only a portion of the sand bed that is deemed to besufficient for filtration operation.

The dislodging member may be described as being at least substantiallyoutside of the bed and preferably completely outside of the sand bed buttouching the sand bed top surface. If the dislodging member issubstantially but not completely outside of the bed, the dislodgingmember may contact the sludge mat M, and optionally the mixed liquorabove the mat, and preferably only up to about 1 inch depth of the sandout of a sand bed that is about 12 inches deep (preferably in the rangeof 8-16 inches). In instances in which the member 10 is completelyoutside of the bed, it is preferably less than about 2 inches from thesurface, more preferably less than 1 inch from the surface, and, mostpreferably, touching the surface. The sludge mat is believed to beginblinding the filter bed surface when it forms in a thickness of greaterthan about ½ inch, and it is believed to be on the order of 2-5 inchesthick in most operations wherein a dislodging blade is not operating.

In a reactor with a properly-operating sand stirring blade, the sand bednormally will be substantially flat, and certainly flat plus/minus 2inches. Because these small variations in sand level are expected,however, the preferred dislodging members preferably ride along thesurface, and up and down with the surface, preferably without plowing orotherwise moving the sand to any significant extent. With greatervariation in the sand level, however, caused by reactor upsets or otherphenomenon, the dislodging members may tend to plow or otherwise movesmall amounts of sand for short distances, for example, for a few incheswhile the blade portion is dragged through a higher hill of sand.Similarly, due to possible “valleys” in the level of the sand surface, ablade portion that normally contacts the sand bed surface may notcontact the surface constantly, or along the entire length of dislodgingmember. Methods of using the invented sludge mat dislodging system maycomprise operating it occasionally, most of the time the reactor isoperating, or continuously.

Referring now specifically to the drawings, there is shown apparatus fora prior method of unplugging a sand filter bed (FIG. 1), and several,but not the only, embodiments of the invented filtration media renewaland control that includes sludge mat dislodging. In FIG. 2, an anaerobicmicrobial sludge blanket reactor 100 is provided with a settled bed ofcourse particulate, at the bottom of the vessel, serving as a filter bedor “sand bed” 14 for filtering the reactor effluent. The courseparticulate may be various compositions, such as 10-40 mesh sand, butbigger or smaller sizes may be used.

The reactor in FIG. 2 illustrates a dual filtration system, comprisingboth a sand bed renewal system 20 and a sludge mat renewal system 10.The sludge mat renewal system 10 comprises at least one sludge matdislodging member at the top surface of the sand, sweeping along the topsurface of the sand bed, preferably in contact with the sand bed but notprojecting into the sand bed and not hanging significantly above thesurface of the bed.

For example, the embodiment shown in FIGS. 2 and 3 includes apaddle-style sludge mat dislodging system 10, in combination with alower, in-sand-bed stirrer blade 20 in a microbial reactor 100. The matdislodging system 10 comprises a single radial arm 12 rotating on anaxis A somewhat above the surface of the sand bed 14. The radial arm 12serves as both support structure for the dislodging members (paddles 18)and as a means for providing fluid flow to reach a propulsion nozzle 11.The radial arm 12 may comprise one or more tubes and other struts, bars,and braces, as needed to provide the structural integrity, shape, andlength needed. The radial arm 12 connects generally at fluid connection16 to a vertical conduit (not shown) that conducts fluid to the hollowinside of the radial arm. Mixed liquor may be pumped through a hollowportion of the radial arm and out of propulsion nozzle 1 in the trailingdirection (into the paper in FIG. 2), thereby powering system 10. Thepropulsion nozzle is preferably at the distal end of the radial arm, butthere may be more than one nozzle located at various radii on the arm. Adual feed swivel system allows fluid flow to the radial arm during armrotation. Dual feed swivel systems may be available from Dynamic Sealingin Minneapolis/St. Paul, Minn., U.S.A.

Dislodging system 10 in FIG. 2 includes a plurality of dislodgingmembers, “renewal paddles” 18, radially spaced along the support arm 12.Paddles 18 hang down from the support arm 12 on one or more flexibleconnectors 24, and are dragged by the radial arm 12 along the topsurface 19 of the sand bed 14. As shown in FIG. 3, the paddles 18 tendto trail the support arm 12, lying on top of the sand bed inside thesludge mat M or where the sludge mat would form if not for the paddlesdisrupting the formation of the mat M. The paddles 18 are adapted insize and weight to ride along the surface of the sand bed but preferablynot to dig into the sand bed or plow the sand bed at any radial armspeed. The preferred jointed (25) or flexible attachment of thedislodging members to the radial arm should be such that the members donot twist out of parallel alignment with the support arm. The dislodgingmembers or the bracket holding one or more of the dislodging members maybe weighted to ensure that the dislodging member(s) do not “fly” upwardsbehind the radial arm instead of resting on and riding on the sandsurface.

Fluid flow through a propulsion nozzle/opening in the trailing side ofthe sludge mat dislodging system is normally sufficient for powering thesystem, but leading side opening(s), as discussed in U.S. Pat. No.6,346,412, may also be used if needed to fluidize the sludge mat infront of the radial arm. As discussed earlier in this description,propulsion flow and/or fluidizing flow should be positioned andcontrolled (preferably, independently) so that solids and the biomasstherein are not shredded/pulverized.

Other dislodging members may be effective, including bars, rods, chains,flaps, nets, or other protrusions or aperturances of many sizes andshapes. The dislodging members may be rigid and/or flexible. Thedislodging members may be connected to their respective carrying arms byflexible, jointed, and/or rigid connections or may extend integrallyfrom the carrying arm. While a flexible or jointed connection ispreferred, a rigid member with a rigid connection may be utilized,especially if the member is sized carefully to ride on the filter bedsurface. In general, it is preferred that the dislodging members arediscrete members that are relatively short (dimension L in FIG. 2) whencompared to the reactor radius, and that are arranged end-to-end inseries along the radial arm with gaps G between the members into whichdislodged sludge may move. Each dislodging member may be attached to theoverhead support structure via a flexible or jointed connector, or, lesspreferably, the dislodging member itself may be flexible/joints, forexample, a flexible rubber paddle.

Most preferably, the dislodging members are shaped so that the sludgemat is moved aside from the path of the dislodging member, althoughlifting the mat so that some of it floats upwards may also beacceptable. Thus, the dislodging member may move sludge mat eithervertically or horizontal. An additional effect of the dislodging of thesludge mat may be to release gas trapped in the sludge mat, which gastends to carry some of the sludge mat material with it upwards into thereactor. This gas-induced sludge mat movement may be a substantial partof the vertical movement of the sludge mat.

The dislodging member substantially or completely uncovers the sandsurface across which it is passing, preferably with 90-100 wt % removalefficiency of the sludge mat as the dislodging member passes over anarea. The sludge mat tends to be pushed over to the sides of thedislodging member and may also float up into the mixed liquor, andsolids from the mixed liquor begin settling down onto the newly-clearedpath within a few seconds after clearing by the dislodging member. Thus,the dislodging member's path is not cleared for very long after thepassing of the member, but the path still may be said to be “cleared”and the clearing step still affects improvement in access of the mixedliquor to the filter bed and in reactor effluent flowrates. In theadjacent “non-dislodged” areas of the sand surface, which are notcontacted by a dislodging member, the sludge mat may actually becomethicker, but the newly-moved sludge will tend not to be as dense as theoriginal mat.

Preferably, multiple arms or arm portions are provided to clear the matand also the newly-moved sludge from the gaps left by the first arm orarm portion. For example, a second, separate arm may move independentlyfrom, or preferably integrally with, the first radial arm but at 180°from the first radial arm. This second radial arm may have dislodgingmembers (the same or different design as those on the first radial arm)that are spaced differently from the central axis compared to thedislodging members on the first arm. Thus, the dislodging members andthe gaps between the dislodging members are staggered/offset, so that,in embodiments in which two arms are 180° from each other, all areas ofthe sludge mat are dislodged at least every half rotation of the arms.Alternatively, a single radial arm may carry front and rear sets ofdislodging units, for example, a front set that dislodges the sludge matbut that leaves gaps, and a second set that follows within a few feet toclear the sludge mat from the front set's gaps.

As discussed above, the invented dislodging system does notsignificantly enhance the reactor effluent flow rate once the sand beditself becomes loaded with solids. Therefore, embodiments of theinvention preferably comprise the sludge mass dislodging system workingin concert with apparatus and methods for backwashing the sand,preferably by stirring and fluidization. Typically, the sludge matdislodging system operates frequently during a remediation run, but thesand bed stirring blade only operates occasionally. The sludge matdislodging system operates without slowing or stopping reactor influentand effluent and without otherwise interrupting operation of thereactor. Back-washing of the sand bed, however, interrupts the reactoroperation, as the reactor effluent must be shut off to prevent massiveloss of biomass out of the reactor. When the sand bed stirring blade isused, the sludge mat dislodging system is normally not used.

In addition to a sludge mat dislodging system and preferably a sand bedstirring system, some embodiments of the invention will also include astirrer blade in the mixed liquor in the main body of the reactor. Sucha mixed liquor stirring blade would be provided at least one foot abovethe sand bed, and preferably from 1-10 feet from the sand bed in a 13-35foot high reactor. Such a mixed liquor stirrer arm would not touch thesand bed and does not disrupt or disperse the sludge mat forming on thesurface of the bed. The distance between a mixed liquor stirrer arm andthe sand bed is too great for the arm to affect any dispersal in thearea of importance, and consequently it does not prevent sludge matformation.

An especially-preferred embodiment of the invention is shown in FIGS.4-9. The microbial reactor 200 comprises a vessel 202, a sand bed 214, aslotted screen 206 generally underneath (or alternatively inside) thesand bed, an outlet 208 for sending filtered effluent out of the reactoras product and/or to storage for later recycle to the reactor. Mixedliquor 209 in the reactor vessel comprises water and solids (food,grease or other BOD and contaminants, and microbes) and optionally otheradditives deemed appropriate for remediation of the mixed liquor.

The sludge mat dislodging system 210 of FIG. 4 comprises two radial arms212, 212′ extending 180° from each other. The radial arms 212, 212′comprise radial portions 213, 213′ and axial portions 215, 215′, whereinthe radial portions are high up in the mixed liquor, for example, about2-4 feet up above the sand bed 214. The axial portions 215, 215′ extenddown within about 1-2 feet of the sand bed, extending around the otherstructure (such as sand blade system 260 and propulsion arm 276) andgenerally ending in radial bars 216, 216′ that hold dislodging units217.

The radial arms 212, 212′ are propelled by propulsion nozzles/openings230, at or near the corner junction between the radial portions 213,213′ and the axial portions 215, 215′. The radial portions 213, 213′ mayalso comprise or support other conduits and outlet nozzles, for example,chemical/nutritive additive nozzles 232. The radial arms 212, 212′ arerotatably supported and supplied with propulsion liquid by dual feedswivel 240. Propulsion fluid supply 242 and chemical additive supply 244are (partially) shown entering the dual feed swivel.

Sand stirring blade system 260 is included in reactor 200, comprising asingle stirring blade 270 with fluidization nozzles 272 pointingpreferably slightly downward and not directly at each other. Thepropulsion nozzle/opening 274 for the blade system 260 is located on anupper radial arm 276 that is rigidly connected to the rest of the sandstirring blade arm but that is significantly higher in the reactor thanblade 270. As discussed above, this locates the propulsion jet up andaway from the sand and the sludge mat, and helps preventsshredding/pulverizing of biomass. The propulsion and the fluidizingfunctions of the stirring blade system 260 are preferably controlledseparately and may use different liquids. Like the sludge mat system210, the sand stirring blade system 260 rotates on a dual feed swivelsystem, which allows for one or more fluid streams through the equipmenteven during rotation.

FIGS. 5-9 illustrate details of the sludge mat dislodging units 217.Each dislodging unit 217 comprises a plurality of V-shaped dislodgingmembers 218 aligned side-by-side on a bracket 219. The bracket 219 ishung by flexible connectors 224 from the radial bars 216. While FIGS. 5and 6 show the dislodging units 217/members 218 extending below the topsurface 280 of the sand, this schematically represents that thecombination of the members 218 and connectors 224 is longer than thevertical distance from the radial bars 216 to the sand surface 280, butthat, in operation, the radial bars 216 drag the dislodgingunits/members slightly behind them so that the dislodging units 217follow at an angle to the sand surface 280 (See FIG. 9).

Dislodging members 218 have a slanted (preferably V-shaped) frontsurface 221 with front ridge 228, and a beveled/slanted bottom surface223 that is at approximately 30 degrees from the ridge 228 (angle Apreferably in the range of 10-45 degrees). The front ridge 228 tends tomove forward through the sludge mat at an angle to the plane of the sandsurface (angle B also preferably 30 degrees and in the range of 10-45degrees) and bottom surface 223 rides/slides generally parallel to thesand surface 280. Therefore, the front surface 221 with its pointedfront extremity (ridge 228) move forward into the sludge mat, pushingthe mat aside via both sides of each member 218. Therefore, thepreferred dislodging member may be said to have at least one generallyvertical side that is slanted relative to the direction of forwardtravel of the member. This way, that at least one slanted side pushessludge to the side relative to the leading edge of the member.

The sludge slides along the front faces (221) of the members 218 andmoves into the gaps G between the members 218 and into the gaps G′between the units 217. This helps prevent the members 218 from pushing alarge amount of sludge in front of them. Instead, the sludge mat isdislodged and moved aside to rest on the mat in gaps G, G′ beside wherethe member 218 has passed. Some sludge may be lifted upwards and/or mayfloat away, but the preferred V-shape dislodging member tends to insteadpush the sludge to the side. These methods produce very little or noshredding or damage to the biomass, and yet they clear and clean largeareas of the sand surface.

Four of the dislodging members shown in FIG. 7 have hollow interiors238, but these interiors do not accumulate sand due to the direction oftravel and the slant of the bottom surface 223. One of the four membersis a solid and/or weighted dislodging member 218′, which brings thetotal weight of the dislodging unit 217 to an appropriate amount todisrupt and dislodge the sludge mat without digging into the sand.Typically, a dislodging unit 217 of the design shown in FIGS. 6-8 weighs5-8 pounds.

FIG. 5 illustrates that the dislodging units 217on one arm 212 areoffset from the radial location of the units 217′ on the opposite arm212′, so that the sludge mat in the large gap G′ left between the units217 may be cleared by the opposite unit 217′. Regarding the smaller gapsbetween the members 218, sludge moves into these gaps, but, due to thefluid movement in the reactor, and the narrowness of these gaps, littlemat builds up permanently in along these gaps and, instead, most of themat eventually moves all the way to the far side edges 248 of the units217, 217′. Thus, substantially all of the sand surface, from the outeredge of the furthest-out member 218 to the inner edge of the closest-inmember 218, is cleared of mat once about every 360° rotation of thesystem.

A control system may be designed to rotate the sludge mat dislodgingsystem as needed or desired, based on pressure drop across thefiltration system (sand bed plus mat), predetermined timing set for aparticular feedstock, or other criteria. Likewise, the control systemmay operate the sand stirrer blade as needed or desired, typically basedon the buildup of pressure drop across the filtration system. Forexample, the dislodging system may be operated most of the time duringoperation of the reactor, for example, 30-45 minutes of every hour, or,for high effluent operations, 45-60 minutes of every hour. Thedislodging system may rotate, for example, about 1-4 rpm, and preferablyabout 2 rpm. The sand blade stirring blade may be operated severalrotations every few hours, for example, for about 4-10 minutes every 4-6hours, or up to about 4-10 minutes every 2-3 hours. The sand stirringblade may rotate, for example, about ¼-2 rpm, and preferably about ½rpm.

FIG. 10 illustrates a plurality of rotary sludge mat dislodging modulesin a single vessel. This may be effective for reactors that are so thata single rotating arm for supporting dislodging members may not bepractical because an extremely long rotating arm would be required.Preferably, rotating arms up to about 15 feet long are preferred, sothat a single rotating arm may work effectively in a vessel up to about30 feet in diameter. For vessels larger than 30 feet in diameter, aplurality of rotating modules may be desirable.

FIG. 11 illustrates an alternative embodiment of the invention wherein asand bed and a sludge mat dislodging system according to embodiments ofthe invention are provided in a filtration vessel in which noprocess/unit operation other than filtration is taking place in thevessel. The invented sludge mat dislodging system may be utilized withor without a sand bed stirring system as desired.

Operations including embodiments of the sludge mat dislodging systemgreatly improve run times between sand bed plugging, as evidenced by thedata shown in FIGS. 12-14.

EXAMPLE I

FIG. 12 shows data from pilot plant operation of an anaerobic sludgeblanket reactor having a sand bed, remediating activated sludge from amunicipal waste facility, characterized by 0.5-3 wt-% solids, percentsolids. Many runs were done, some with and some without a sludge matdislodging system in operation (also known as the “rake”), and withoutany sand blade stirring or other backwashing. Reactor effluent flowratedata was taken every five minutes. A fresh sand bed, given the providedslotted screen and reactor effluent piping, was capable of a maximumreactor effluent flowrate of about 6 gpm.

In the runs without the rake (without sludge mat dislodging), reactoreffluent dropped quickly from the maximum of 6 gpm to a small fractionof that flow. For example, in the runs without the rake in operation,the reactor effluent dropped to ⅓ of the maximum flow (about 2 gpm)within less than half an hour. By the time two hours had elapsed, theflowrate had dropped to less than 1 gpm, or less than ⅙ of the originalflow.

On the other hand, in runs including operation of the rake (with sludgemat dislodging), the reactor effluent dropped much more gradually, from6 gpm to 4 gpm over periods ranging from about 3 to 12 hours. Only after10+ hours did reactor effluent drop to as low as 2 gpm. In all of therake-on runs, the reactor effluent performance was sufficient to allowat least four-hour runs without reaching reactor effluent flowrates thatwould make sand bed backwashing necessary and desirable. The rake-onruns were done with continuous operation of the rake, but intermittentoperation of the rake would also produce acceptable run lengths inbetween backwashing.

FIG. 13 plots the same data as shown in FIG. 12, but only the first fourhours of each run, given the fact that a four-hour run beforebackwashing is a reasonable and desirable operation mode. Clearly, in afour-hour run, the operations without the rake produced unacceptableresults, wherein the reactor effluent dropped below acceptable rateswithin the first half hour. The operations with the rake producedacceptable results, wherein the reactor effluent stayed at acceptablerates and were greater than 50% of the original flowrate for the entirefour hours.

EXAMPLE II

An extended operation was performed using the reactor and activatedsludge feed of Example I, with substantially continuous rake operationbetween sand bed backwashings via a sand bed stirring system. Data fromthis operation is plotted in FIG. 14. This operation was repeatedseveral times, with various percentages of the slotted screen(“underdrain” underneath the sand bed) open, to test the effect of theamount of underdrain in use in the reactor. Each cycle (from beginningof reactor operation to the time of shutting off reactor effluent andbackwashing) was approximately four hours. The data shows that, duringeach cycle, reactor effluent stayed at acceptable levels, slowlydropping from approximately 6 gpm to approximately 3 gpm. The data showsthat, after each backwashing of the sand bed, the flowrate went up to,or very near to, the original flowrate of 6 gpm. Many cycles weresuccessfully performed, illustrating the long-term feasibility andoperability of a sludge blanket reactor using a filter bed incombination with the invented technology.

Thus, the invented methods of operation include rotating or otherwisemoving a dislodging member through at least a portion of the sludge matarea on top of a filter bed in a vessel/reactor. Preferably, the methodsinclude operating the dislodging system during normal operation of thereactor, that is, during influent flow of wastewater, effluent flow offiltered water, and ongoing microbial remediation of the waste solids inthe mixed liquor. Thus, the invented methods and apparatus are forongoing use during the process, rather than for use during maintenanceduring shut-down. Preferably, the invented methods comprise dislodgingthe sludge mat but not removing it from the reactor. Preferably, themethods also include repeated cycles of downflow reactor/vesseloperation with a dislodging member operating at least part of the timein some or all of the cycles, wherein the cycles are defined by the timebetween backwashings of the filter bed.

Embodiments of the invented methods may be beneficial in many differentremediation operations. For example, the invention may be used withprocess feeds containing contaminants consumed quickly by the providedmicrobes. For example, feeds in the range of 1000 mg/L up to 50,000 mg/LBOD require reactor residence times of only 12-48 hours, and a reactorfor such an operation would typically be designed for high effluent flowrates in the range of 0.5 to 4 days of hydraulic residence time. Thismay be compared to effluent flow rates in the range of 5-12 days ofhydraulic residence time for wastewater containing greater than 50,000mg/L BOD. With the invented sludge mat control and renewalmethods/operation, a high flowrate operation of 0.5-4 days hydraulicresidence time is achievable and practical.

The instant invention may be applied to feeds containing a wide range ofsuspended solids. High TSS and/or FOG reactors, anaerobic or aerobicreactors, sludge thickeners, municipal water filtration for raw river orlake water, or tertiary waste treatment of sewer water containing aslittle 30-50 ppm solids, may all benefit from the instant invention.With the instant invention, anaerobic remediation of greater than 1000mg/L TSS may be achieved with 95-99% removal of BOD. Embodiments of theinvention may process, for example, up to about 100,000 mg/L of TSS andFOG. In such an operation, a longer residence time (of 5-12 days) istypically needed, but acceptable cycle times (preferably about 4-12hours) may be achieved in spite of the very high solids in the reactorand the resulting high probability of a heavy/thick sludge mat forming.While the filtration and effluent systems of many sludge blanketreactors may be considered effective if they are producing 0.1 galreactor effluent per sq. ft/minute, the instant invention may greatlyincrease this throughput to at least 0.2-0.4 gal reactor effluent persquare ft/minute.

Although this invention has been described above with reference toparticular means, materials and embodiments, it is to be understood thatthe invention is not limited to these disclosed particulars, but extendsinstead to all equivalents within the broad scope of this descriptionand the following claims.

1. In a downflow vessel containing a filter bed having a top surface and containing liquid comprising solids that settle on said top surface, the vessel further having a vessel effluent outlet in or beneath the filter bed, the improvement comprising: a dislodging member in the vessel adapted to move across said top surface to dislodge a portion of said solids that settle on said top surface, to uncover at least a portion of said top surface for access by said liquid so that liquid flows through the filter bed and to the vessel effluent outlet; and wherein the vessel is a sludge blanket reactor and the liquid comprising solids is mixed liquor being microbially-remediated in said reactor.
 2. In the vessel of claim 1, the improvement further comprising an arm that rotates on a plane generally parallel to said top surface, wherein the dislodging member is pivotally connected to the arm.
 3. In the vessel of claim 1, the improvement further comprising an arm that rotates on a plane generally parallel to said top surface, wherein the dislodging member is flexibly connected to the arm.
 4. In the vessel of claim 1, the improvement further comprising an arm that rotates on a plane generally parallel to said top surface, wherein the dislodging member is rigidly connected to the arm.
 5. In the vessel of claim 1, the improvement further comprising the dislodging member being V-shaped and having a front ridge for moving forward into the solids on the top surface.
 6. In the vessel of claim 1, wherein the solids settling on said top surface form a sludge mat of 2-20 wt-% percent solids in water and the dislodging member moves through and dislodges the sludge mat.
 7. In the vessel of claim 6, wherein the filter bed is particulate selected from the group consisting of sand, pebbles, and carbon.
 8. In a downflow microbial waste remediation reactor containing mixed liquor comprised of water, waste solids, and microbes, and the reactor having a filter bed with a filter bed top surface upon which a portion of said waste solids and microbes settle to form a sludge mat, the improvement comprising: a sludge mat dislodging system comprising a member positioned at or near said top surface in contact with the sludge mat and adapted to move generally parallel to the top surface through the sludge mat in a direction of forward movement to dislodge at least a part of the sludge mat from the top surface.
 9. In the reactor of claim 8, the improvement further comprising the member being adapted to have at least one generally vertical side that is at an angle to the direction of forward movement so that it is adapted to push sludge mat aside.
 10. In the reactor of claim 9, the improvement further comprising the member being V-shaped.
 11. In the reactor of claim 8, the improvement further comprising at least one arm rotatably mounted in the reactor, and said dislodging member being connected to the arm so that the arm moves the member through the reactor.
 12. In the reactor of claim 11, the improvement further comprising two of said arms, wherein each of said arms comprises at least one of said dislodging members.
 13. In the reactor of claim 8, wherein the mixed liquor comprises less than 2 wt-% solids in water and said sludge mat is 2-20 wt-% solids in water.
 14. A method of operating a sludge blanket microbial reactor to remediate a waste stream, the method comprising: providing a filter bed with a top surface in a reactor; providing a mixed liquor in the reactor comprising water, suspended solids, and microbes, wherein some of said suspended solids and microbes settle out of solution onto the top surface of the filter bed to form a sludge mat that is relatively dry compared to said mixed liquor, wherein the sludge mat restricts flow of liquid into the filter bed; moving a dislodging member across the top of the filter bed in a path to dislodge said sludge mat from said path, so that liquid can access the filter bed for filtration and exit the reactor; wherein said moving a dislodging is done while said waste stream is flowing into the reactor and liquid effluent is exiting the reactor.
 15. A method as in claim 14, further comprising providing an arm carrying the dislodging member, and rotating the arm in the reactor generally parallel to the top surface.
 16. A method as in claim 15, wherein rotating the arm comprises pumping liquid through a propulsion opening in a trailing side of the arm.
 17. A method as in claim 15, wherein moving said dislodging member comprises pulling a top portion of said member forward with said arm so that a lower portion of said member slides along the filter bed behind the arm.
 18. A method as in claim 14, further comprising providing a filter bed stirring member inside the filter bed, and intermittently stirring the filter bed with the stirring member.
 19. A method as in claim 18, comprising operating the reactor in a first period comprising said moving the dislodging member across the top of the filter bed and comprising a second period comprising stopping said moving of the dislodging member, stopping liquid flow out of the reactor from the filter bed, and performing said stirring of the filter bed to fluidize the filter bed.
 20. A method as in claim 14, wherein the dislodging member is V-shaped with a ridge and two slanted sides and wherein moving the dislodging member comprises moving the member so that the ridge moves forward into the sludge mat and the sludge slides aside on said two slanted sides. 